Hi Nicky
This is what I have researched from the FAQ section.

How do I get more STEEM Power?
With STEEM tokens in your wallet, click "Power Up" to turn them into STEEM Power. If you have Steem Dollars, you can convert them to STEEM from your wallet, and then power up the STEEM.

If you don’t already have STEEM or Steem Dollars in your wallet, you can purchase them using bitcoin (BTC), ether (ETH), or BitShares (BTS) tokens. You may purchase BTC on various exchanges, such as Coinbase.com or Localbitcoins.com.

To buy:

Click "Buy Steem" from the main menu in the top right corner of Steemit.com, or from your wallet.
Select the currency to deposit, and enter the amount of that currency you wish to use.
Enter your Steemit account name (without the @) for "Your receive address".
Click the "Get Deposit Address" button.
Send the currency to the provided address.
STEEM purchases made via Steemit.com are facilitated by BlockTrades.